I’ve got the power! Part 1: Windows 7 vs XP

One of the advertised benefits to schools of upgrading to Windows 7 has been the improved power management, which when used correctly, will decrease the power usage of computers throughout the school estate. But how is that actually achieved? A lot of people, myself included, assumed that the bulk of the savings would come from better Group Policy support to implement power saving schedules, such as transitioning to Sleep mode after a set time.

Not so.

While that does help, there are significant benefits even without power management schedules. Simply put, Windows 7 uses less power. I measured the power usage of two computers; identical hardware, but with different software. One ran an RM CC3 build using Windows XP, the other ran Windows 7. Both machines were production workstations with all the normal software I install on them, and they were tested while idling at the logon screen. The machines themselves were 2009 Dell OptiPlex 360 workstations, and the power usage was measured using an in-line mains meter. I did not measure the monitor power usage.

Here’s what I found:

OS

Idle

Sleep (S3)

Windows XP (CC3)

55.0 W

41.1 W

Windows 7

45.0 W

1.7 W

There are two lessons here: firstly, Windows XP is shockingly bad in sleep mode. Given that XP came out in 2001, this shouldn’t be entirely surprising, but I was still astonished by how high the power usage remained even when the machine was supposedly in its low-power mode. To an observer, the two machines were indistinguishable from each other at this time – power LED blinking, fans off, silent operation – but the difference in power usage was outrageous.

The second lesson appears to be that Windows 7 draws less power when you’re not using it. Later on I tested both machines using a CPU stress test, and they pulled the same amount of power, but when left idle, the Windows 7 machine averaged 10W less.

I should note that it’s entirely possible the RM background tasks were responsible for the latter discrepancy; I didn’t have a non-RM XP machine to test. No such difference could explain the sleep mode difference. Similar results emerged on different hardware, so this didn’t appear to be an anomaly with the Dell machines.

So, how much is that in cold hard cash? We’ll look at some more surprising results in part 2 later this week.

7 responses to “I’ve got the power! Part 1: Windows 7 vs XP”

The S3 sleep situation sounds more like a bug in the specific hardware/driver configuration, rather than a general XP issues.

XP needed a lot of additional tools an driver in order to utilize all power saving features correctly. A better comparison would be against an original Dell XP Preload, which in theory at least should include working power management.

It happened on some 2yo RM-branded hardware too, so it wasn’t exclusive to the Dell I posted figures for. I will take a look to see if the ones I tested are missing any power management drivers though.